The ANDES E07K sports a much warmer sound signature with an accentuation in the mid bass and a slight smothering of the vocals in where they become a bit too 'warm' and smooth. The E18 gives you a more balanced vocal range, and a more controlled bass along with a clearer sound signature that has qualities similar to an O2, but it has problems in the upper mid range, and high range with sonic fluctuations and deficiencies that may make it more analytical for some headphones.

The two units are quite different in their functions, although the E18 can also be a computer and portable DAC/amp. I would go for the E18 if you want a higher quality sound (at a loss of cohesion) and want to make use of its Android features. I would go for the ANDES if you want a funner sound, don't have as much money for the E18, take a gamble at trying to get it to work with Android devices (it is known to work with some), and want a device of that size.

I find the E18 to be quite lean and punchy. If your Sennheiser has the typical warmish Sennheiser sound they might pair quite well. I'm sorry I can't be more specific but I've not heard your particular headphones. What are you going to be hooking up to the DAC?

Will the effect be really obvious ? Because i tried JDS Labs C5D and i hear no different.

You know, depending on your source and how bad/good it already is, "obvious" is not the first word that comes to mind when testing a DAC specially in your case that you already tried one without noticing anything. To me DAC is something that takes more of a "trained" ear. Not having a super ear, we all pretty much have the same capacity but knowing what you are listening for. Also your files will be important of course. You want high quality files like 320 mp3 or higher to get the most of it.
I do agree Zorrofox on his description of the E18 sound.

Z ultra worked with creative omni usb in my case
I cant tell either was it digital out ro jusrlt forwarded analog through usb cable
But it worked with poweramp and very well.... Only thing wqs that it was recognised as external keyboard and i couldnt use another keybord...no typing possible with external dac
Maybe possible and i couldnt solve that